Characterization of Fluidization Quality in Fluidized Beds of Wet Particles

Monitoring the fluidization quality represents an operating challenge for many processes in which a liquid is sprayed into a gas-fluidized bed, such as fluid coking, fluid catalytic cracking, gas-phase polymerization, agglomeration and drying. Although the presence of liquid will generally have an adverse effect on fluidization, there are often strong incentives in operating with high liquid loadings. For the fluid coking process, for example, operating at lower reactor temperature increases yield and reduces emissions but increases the bed wetness, which may lead to local zones of poor mixing, local defluidization and a reduction in fluidization quality, compromising the reactor performance and stability. The objective of this study is to develop reliable methods to quantify the effects of liquids on fluidized beds.This study examined several methods to evaluate the fluidization quality. Each method was tested in a 3 m tall column, 0.3 m in diameter. Bed wetness was achieved with an atomized spray of various liquids, spanning a wide range of liquid properties.The introduction of liquid in a fluidized bed may result in the formation of wet agglomerates that settle at the bottom of the bed. The liquid may also spread on the particles, increasing their cohesivity and reducing the bed fluidity.Several experimental methods were developed to characterize the effect of liquids on fluidization. Some methods such as the falling ball velocity or the detection of micro-agglomeration from the entrainment of fine particles, are unaffected by agglomerates and detect only the change in bed fluidity. Other methods, such as deaeration or the determination of bubble size from the TDH, are affected by agglomerate formation and changes in bed fluidity.

Entrainment and Stability of a Horizontal Gas-Liquid Jet in a Fluidized Bed

Fluid coking is a non-catalytic process where heavy hydrocarbon feed, sprayed using jets into a fluidized bed reactor, cracks upon contacting hot coke particles and produces valuable volatile fractions. It is estimated that the Alberta tar sands contain 1.7 trillion barrels of oil, equivalent to 35% of the world’s crude oil reserves, of which the majority is processed using fluid cokers. Important parameters that affect the yield of fluid cokers include the feed jet stability and therefore its ability to entrain and mix the injected feedstock with the fluidized coke particles. To this purpose, this study investigated the effect of the use of various types of draft tubes, placed downstream of the feed jet to enhance mixing, on solids entrainment and jet stability.Specifically, it has been demonstrated with the use of a gas-liquid and gas-only jet that an optimum distance exists between the nozzle and draft tube for entrainment of solids. For both cases, this optimal distance occurs as the jet touches the draft tube wall. However, for a gas-only jet this occurs at a shorter distances due to the increased angle of expansion. The angles of expansion were confirmed using triboelectric probe measurements. It has also been shown that the shape of the inlet to the draft tube will have an effect on the rate of solids entrainment as will the presence of pulsations in the jet.